It is known in the art to stabilize the speed of a DC motor at a set reference value by monitoring the power that is fed into the motor in accordance with the deviation of the actual motor speed and a preset reference speed. Speed stabilizing devices are added to a DC motor driver in order to determine said deviation and to increase or decrease the applied power correspondingly.
One group of commonly used speed regulating devices comprises analog electronic circuits. Inherent to analog electronic components are component spreading, temperature drifting, amplifier offset, thermal dissipation and corresponding response fluctuations. These inaccuracies have an influence on the stability of the reference speed indicating signal and affect the properties of the incorporated components.
Pulsed-signal systems overcome the drawbacks of analog systems because of their higher noise margins, i.e. their minor sensitivity to signal level fluctuations. Furthermore, they enable the use of an accurately defined reference clock signal indicative of the reference speed.
The prior art pulsed-signal speed stabilizing methods lack optimization for various setable speed values and variations of the DC motor characteristics.
Inaccurate speed regulation might come forth from the replacement of one DC motor by another specimen not having an identical transfer characteristic. Furthermore, oscillation might come forth from stabilization attempts at other speed values than the reference speed for which the circuit was designed. This last-mentioned inconvenience will be explained furtheron.